1. Field of Invention
The present invention is related to a technology of bio-chip, and more particular to a bio-chip using the surface acoustic wave (SAW) mechanism, capable of detecting a bio sample.
2. Description of Related Art
The surface acoustic wave (SAW) technology has been used in wide application. According to its design mechanism, it can be used to detect various changes in physical or chemical properties, and can be used to design a detector for detecting, for example, temperature, pressure, twist, or even the volatile of gas or chemical material.
Certainly, the SAW apparatus can also be used in bio-chemical or biomedical detection. Due to the design with high sensitivity and simple structure, the SAW apparatus has been well considered in applications. Generally, the SAW apparatus needs to be covered with a bio-recognition coating layer for detecting the bio sample, such as a specific bio-chemical or biomedical material.
In the bio-chemical or bio-medical field, several type of biomarkers have been known to help the estimation or diagnosis of various diseases or the relating symptoms. As a result, the prevention or precaution on developing or worsening of diseases can be made. For example, the status of cardiovascular diseases can be estimated or diagnosed by using markers of CK-MB (CK, Myoglobin) and Troponin-I/T. If the Troponin-I/T is the sample to be detected, generally, since the concentration of Troponin-I/T in blood is very low, it therefore needs to be detected by a sensor with high sensibility. However, in the conventional technology, the detecting sensibility for the Troponin-I/T is relatively low. This conventional technology for detecting the Troponin-I/T still has disadvantages to be further solved.
Reviewing the prior art, U.S. Pat. Nos. 6,321,588; 5,306,644; and 5,992,215 have disclosed relating detection tools in combination with SAW for signal amplification. The signal is then detected by circuit. These prior arts are concentrating on analyzing the chemical material and gas molecules. Although the U.S. Pat. No. 4,598,224 also discloses a relating technology but the quantity analysis and noise treatment are not considered. The publications or published patents are generally on the application of communication and high frequency device but not on the application of bio-sensor. In addition, some of them may be used to detect the micro change in physical quantity, such as analysis of existence of gas or chemical material in small quantity.
In addition, the conventional SAW apparatus can use, for example, the Inter-Digital Transducer (IDT) design. The publication of “The 30th Annual Conference of the IEEE Electronics Society, Nov. 2-6, 2004, Busan, Korea; pp 1546-1549” by Gi-Beum Kim et al. has also introduced the SAW sensor. The SAW sensor includes the IDT's on a piezoelectric substrate. The IDT's are formed from thin metal film. When an electric signal with appropriate frequency is applied to the input IDT, SAW is launched on the surface of the substrate due to the reverse piezoelectric effect. The SAW propagates across the surface of the substrate and is converted back into an electric signal by the output IDT. The operating frequency f, is determined by the IDT finger spacing ωs, finger width ωf, wavelength λ, and SAW velocity νs according to the relation of f=νs/λ where λ=2(ωs+ωf). The SAW velocity However, if a mass load is disposed on the path of the SAW, the SAW velocity νs∝√{square root over (c/ρ)} is proportional to the elasticity and density of the substrate and the associated mass load on it. Therefore, the mass load can be detected. The detail can be referred to Gi-Beum Kim et al. and can be understood by the person with ordinary skill. The further detail is omitted here.
However, due to the improper implementing structure of IDT in the SAW apparatus, the performance is not good and could be affected by the noise and echo phenomenon, and then the discerning capability and sensitivity get low. Since the quantity analysis in micro-amount is strongly needed in the current trend, it is strongly desired to have high precision with the least amount of sample.
The conventional design of IDT sensor has many disadvantages, such as easily producing noise. Since the IDT is very sensitivity, the surface is easily affected resulting in several issues. For example, the IDT cannot be integrated into an integrated circuit and it is not easy to handle on property under batch production. As a result, the development is quite limited. In these reasons, some experts in this field change the concerning point and develop the applications of SAW technology on the electronic filter. This technology has been developed for about half century. The efforts from experts on developing this technology are not much in recent years. However, based on the IDT mechanism, the bio-chip with better performance is still needed in continuous development.